feat(api): tiered cumulative quota + self-service registration

Anonymous callers get a free cumulative quota (1000 calls per IP); once
exhausted they get 403 quota_exhausted and must register. Public users can
self-register (email+password) to obtain a higher-quota API key, view usage,
and regenerate the key. Quota counters live in Redis; the public API stays
read-only except for the registration writes.

- migration 0011: app_user table + api_key.quota_total + 'registered' tier
- ratelimit: IncrTotal/TotalUsed/CopyTotal lifetime counters
- middleware: enforce cumulative quota + X-Quota-* headers
- store: RegisterUser/Authenticate/RegenerateKey (bcrypt)
- handlers: POST /api/v1/register, /account, /account/regenerate
- admin: quota_total column + registered tier
- public: 'API 密钥' account page + API docs quota section

Co-Authored-By: Devin AI <158243242+devin-ai-integration[bot]@users.noreply.github.com>

api/internal/handler/openapi.json

@@ -10,7 +10,8 @@
   "tags": [
     { "name": "products" },
     { "name": "catalog" },
-    { "name": "meta" }
+    { "name": "meta" },
+    { "name": "account" }
   ],
   "security": [{ "ApiKeyHeader": [] }, { "BearerKey": [] }, {}],
   "paths": {
@@ -114,6 +115,35 @@
         "parameters": [{ "name": "id", "in": "path", "required": true, "schema": { "type": "string", "format": "uuid" } }],
         "responses": { "200": { "description": "Source" }, "404": { "$ref": "#/components/responses/NotFound" } }
       }
+    },
+    "/register": {
+      "post": {
+        "tags": ["account"],
+        "summary": "Register an account and issue an API key",
+        "description": "Self-service registration; returns the plaintext API key exactly once.",
+        "security": [],
+        "requestBody": { "required": true, "content": { "application/json": { "schema": { "type": "object", "required": ["email", "password"], "properties": { "email": { "type": "string", "format": "email" }, "password": { "type": "string", "minLength": 8 } } } } } },
+        "responses": { "201": { "description": "Account created; plaintext key returned once" }, "400": { "description": "Invalid email or weak password" }, "409": { "description": "Email already registered" } }
+      }
+    },
+    "/account": {
+      "post": {
+        "tags": ["account"],
+        "summary": "View account key metadata and cumulative quota usage",
+        "security": [],
+        "requestBody": { "required": true, "content": { "application/json": { "schema": { "type": "object", "required": ["email", "password"], "properties": { "email": { "type": "string", "format": "email" }, "password": { "type": "string" } } } } } },
+        "responses": { "200": { "description": "Account info with quota usage" }, "401": { "description": "Invalid credentials" } }
+      }
+    },
+    "/account/regenerate": {
+      "post": {
+        "tags": ["account"],
+        "summary": "Revoke the current key and issue a new one",
+        "description": "Cumulative usage carries over; returns the plaintext key exactly once.",
+        "security": [],
+        "requestBody": { "required": true, "content": { "application/json": { "schema": { "type": "object", "required": ["email", "password"], "properties": { "email": { "type": "string", "format": "email" }, "password": { "type": "string" } } } } } },
+        "responses": { "200": { "description": "New plaintext key returned once" }, "401": { "description": "Invalid credentials" } }
+      }
     }
   },
   "components": {